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Expense Splitter

Expense Splitter is a sample HarmonyOS app that makes it easy to record shared expenses. Using predefined participant labels and a simple number pad, you can quickly add payments and see how much each person has contributed.

Preview

Use Cases

• Trip Tracking: Start a trip (e.g., Weekend, Dinner, Taxi) and add participants with predefined labels.
• Quick Expense Entry: Record payments with a simple number pad and assign them to a payer.
• Daily Overview: See on which days expenses were made during the trip.
• Contribution Summary: View how much each participant has paid in total.
• Sample Learning Project: Explore ArkTS + RDB data persistence, UI design for wearables, and expense aggregation logic.

Technology

Stack

• Languages: ArkTS, Typescript
• Frameworks: HarmonyOS SDK 5.1.0(18)
• Tools: DevEco Studio Version 5.1.0.828
• Libraries:
  • @kit.ArkUI
  • @kit.AbilityKit
  • @kit.PerformanceAnalysisKit
  • @kit.BasicServicesKit
  • @kit.ArkData

Persisting RDB Store Data (ArkData)

This project uses relational database (RDB) store (@kit.ArkData) with migrations, CRUD, and predicates for managing expenses.

• Migrations – Stepwise upgrades (0→1→2→3) with PRAGMA user_version, run inside transactions.
• Inserting – Adds expenses and splits amounts into exact cents.
• Deleting – Cascade deletes (removing a trip also removes participants and expenses).
• Updating – Simple updates (e.g., amounts); complex edits handled by re-adding rows.
• Predicates – RdbPredicates and querySql used for filters, joins, and aggregations (e.g., SUM per payer).

Example files:

• src/main/ets/database/RDBBuilder.ets – RDB builder, builds the database + handles migrations + initial RDB creation
• src/main/ets/database/AppDatabase.ets – CRUD, managing trips and payers functions
• src/main/ets/database/migrations/Migrations.ets – Migrations
• src/main/ets/database/tables/ – RDB Tables, creation queries + table columns

Dependency Injection (Registry-Based)

This project includes a lightweight, custom Dependency Injection (DI) system, implemented with decorators and a central service registry.

• Services are registered in MainRegistry.ets using @Register() decorators
• Classes can @Resolve() dependencies without manually wiring them
• Lazy and singleton services are supported via internal ServiceRegistry.ts

Example files:

• src/main/ets/di/MainRegistry.ets – Application-level service registration uses @Register to register a service.
• src/main/ets/registry/Injectable.ts – Injectable Interface, used to mark any class that will be injected later.
• src/main/ets/registry/ServiceRegistry.ts – Core service container, also has @Register, @Resolve decorators.

This allows separation of concerns and improved testability for components like:

• AppDatabase with it's implementation class AppDatabaseImpl
• ViewModels and utilities

Directory Structure

├── entry/src/main/ets/
│   ├──components/                      // Reusable UI components
│   ├──constants/                       // Constants like sizes
│   ├──database/
│   │  ├──migrations/             
│   │  │  ├──Migrations.ets             // Migration steps (0→1, 1→2, …) with RDB query changes
│   │  │  └──RDBMigration.ets           // Migration class definition (from, to) version, with run query method.
│   │  ├──tables/                        
│   │  │  ├──ExpensesTable.ets          // Expense table schema, indexes and columns
│   │  │  ├──RDBTable.ets               // Common table interface for create + indexes + columns
│   │  │  └──TripTable.ets              // Trip table schema, indexes and columns
│   │  ├──AppDatabase.ets               // Database abstraction (methods for CRUD + queries)
│   │  ├──AppDatabaseImpl.ets           // Implementation of AppDatabase using RDB APIs
│   │  └──RDBBuilder.ets                // Builder utility to open DB, apply migrations, build tables
│   ├──di/                              // DI container and main registry
│   ├──entryability/
│   │  └──EntryAbility.ets              // Main entry point ability
│   ├──entrybackupability/
│   │  └──EntryBackupAbility.ets        // Backup entry ability
│   ├──model/                           // Data models (Expense, Trip, TripExpenses)
│   ├──myabilitystage/
│   │  └──MyAbilityStage.ets            // Custom AbilityStage for config setup
│   ├──pages/
│   │  ├──AddExpensePage.ets            // UI for creating a new expense
│   │  ├──AddTripPage.ets               // UI for creating a new trip
│   │  ├──ExpensesPage.ets              // UI showing all expenses for a trip
│   │  ├──Index.ets                     // App start page / navigation root
│   │  ├──PayerExpensesPage.ets         // UI showing expenses filtered by payer
│   │  └──TripsPage.ets                 // UI listing all trips
│   ├──registry/                        // Decorators and DI service registry
│   ├──utils/
│   │  └──Logger.ets                    // Logging utility
│   └──viewmodel/
│      ├──datasource/                   // Data sources feeding ViewModels with prepared arrays (refresh, delete, add) data
│      ├──AddExpenseViewModel.ets       // Handles state & logic for adding a new expense
│      ├──AddTripViewModel.ets          // Manages trip creation flow
│      ├──ExpensesViewModel.ets         // Provides expenses list and summaries for a trip
│      ├──PayerExpensesViewModel.ets    // Exposes expenses filtered by a specific payer
│      └──TripsViewModel.ets            // Handles trips list

Constraints and Restrictions

Supported Devices

• Huawei Watch 5

License

Expense Splitter is distributed under the terms of the MIT License. See the license for more information.